I need help. When I drive in neutral, my rpms stay at about 1500, then when I come to a complete stop it rests slowly back at normal 1000 rpms. I bled the coolant 3 times. I have checked for vacuum leaks many times. I've tried replacing the iacv, and my d15b engine does not have a fitv. If I take of the iacv and close off those holes the car dies. I have tried moving the idle screw and it seems to work at times, but the engine shakes and the car shuts off sometimes. Ive tried messing with the distributor timing and that doesn't do much either. I know I have tried other things as well, and I'm tittering on whether I should buy a new iacv as the one I replaced it with was a used one, but I doubt its that because it did the exact same thing when I used both iacv. I'm also thinking it might have to do with the transmission, I just remembered I changed the speed sensor but that wasn't the issue either, but I'm wondering if something is wrong with the transmission that is not disengaging the clutch all the way causing the idle issue. I thought it might also be the coolant temp sensor or another sensor perhaps. I had one code which was the intake air temp sensor, but I wired it right and took of the code. I also thought it might be the timing belt as I thought it might have some looseness to it when I put it back on. The car runs great, and I'm at the point where I just want to throw in the towel and leave it be and drive it as is.

 

You will now have to do the "set base idle" procedure as you have messed with your idle screw.

All three motors I've had in my car acts just like yours, when moving the idle doesn't drop as low as when you come to a stop.

Your base idle of 1000 sounds high, it should be 720 +/- 50. But the behavior sounds accurate.

 

After setting the base idle, am I correct by saying that I would then have to run the car for 45 minutes to completely set it? I remember reading that some where...

 

How To Adjust Honda Civic Idle Speed - My Pro Street so I looked this up, and the article says that if I disconnect my IACV and it solves the surge then I need a new IACV. I feel that this might be my case as I noticed that yes, it idles near 1000 and doesn't bounce around, but as I give it gas it will bounce slightly up and down how ever high the rpms go. By this I mean if I go up to 3000 rpms it will bounce ever slightly to say 3100 and down to 3000 and then up etc... I'm not about to shell out 180 for a new one unless absolutely necessary.

 

A variance of 100 rpm is not bouncing idle.

A roaming variance of 1000 or more rpm is a bouncing idle. A slight fluctuation of 100 RPM is nothing.

When setting base idle, you cannot use the tachometer of the car.

 

I switched the IACV for the third time. It gave me an OK idle, did not bounce like the last idle air control valve did. With the old IACV, after giving it gas it would go down to 1000 rpm's then bounce to 1500 and not settle back down until I came to a complete stop. With the new IACV it worked almost perfect, went up and then it would go down without fluctuating but it went too low though, about 200rpm's. It was dirty as well so after I saw that the idle was coming down to 200 rpm's I told my self why not clean it, might fix it. It was really dirty, like i doubt any air was passing through the side with the metal mesh filter. After cleaning it, it would just die, turn on and then not be able to hold an idle. That is when I noticed the idle screw was set to all the way closed. I've heard of Honda owners closing off the IACV all together with a block off plate. I tried doing that, blocking it off but it would just turn off on me, was there something special that I needed to do to block off the plate like set the screw to all the way closed or something? So when I cleaned the IACV and messed with the idle screw, backing it off from all the way closed then I succeeded in going back to step one, up to 1500 rpm's while driving and going back down to 1000 when stopped at a red light. If I try to go lower on the idle screw to correct the 1500 rpm's idle, it idles to low when I'm at a stop and then just dies. I've replaced the throttle body with different MAP and and TPS sensors and its only when changing the IACV that it gives me somewhat different results. I am really leaning on finding a way to block off the plate, I will be looking that up or if someone reads this and can tell me the proper way of doing it without having the car shut off that would be great. Thank you in advance for any help.

 

You are running around blindly.

So you found yourself a working IACV. Now you have to set base idle. As well, I will say it again...

You can NOT use the dashboard tachometer for setting base idle. You have to use an external tachometer like a laser tach to set base idle.

Until you do this, you are blindly messing about with no real hope of fixing your issue.

 

Car info? Manual or automatic, OBD1 or OBDII, three-wire IACV or two-wire

If Honda designers had a way to make the car run right with no IACV, they would come from the factory that way. (Blocking off the FITV is kind of common and not an issue at all if you live in a warmer climate.)

 

I think I forgot to mention, you might also re-purge the cooling system. Air pockets will also cause surging idle. Once you get a steady idle, then you have to set base idle since you messed it up.

50 bucks says you still have an air pocket in your cooling system.